Automatically balanced rotor assembly



Dec. 29, 1953 G. RATHMAN l 2,654,304

AUTOMATICALLY BALANCED ROTOR ASSEMBLY Filed Dec. 20, 1950 2 Sheets-Sheet 1 al @a 1? "il- Q6 l a Filol,

INVENTOR A BY A ,M lfm-nv ATTORNEYS Patented Dec. 29, 1953 UNITED STATES PATE-NT OFFICE AUTOMTICALLY BALANCED ROTOR ASSEMBLYl GilbertRathman, Union, N. J., assignor, by mesne assignments, to Dresser Industries, Inc., ,.a, cor-A poration of Pennsylvania Appiicationfeeember 20, 1950, Serial N 0.201,828 .z

compressing gasto relatively high pressures, the.

heatof the gas.causes'thealuminum rotor bcdy to expand-more than the lsteelfshaft and to beeornefloose thereon, thereby unbalancing the rotor assembly.` n'fthevcaseofrv an axial ow machine, the undesirable eilects ofthe unbalance "are aggravated because the expansion of vtheparts willbe-greater-at one end of the rotor 'than at A"the other.

tis therefore the principal object of the present invention t provide novel means-'for automatically maintain-ing` therotative balance of rotor assemblies for Huidy handling apparatus v which embody metal parts having'diiferent heat expansion char'acteristicsand which areeiqcosed to relatively high temperatures during operation.

Another object is to provide a unique construction for `centering thefrotcr body and shaft nf'ajrotary gaspump or-similar device which is so designedas to automatically correct any unbalance in' therotor assembly due to unequal expansion of the parts.

fu'rther object is to provide-a mechanically simple' self-centering connection between a separately formed rotor bodyand lits shaft which effectively prevents the rotorbody from becomv in'gloose'on theshaft'in the event that the bore Osaid" body should become-larger than the shaftV under th'en'iluence of heats These and other objects will appear more iul'y upon" consideration y oi` the `detailed ydescription of=the embodimentsof theiinvention which i ollows.' AlthoughV only toispecic examples of structures'incorporating thein'vention are described and` illustrated in' the accompanying drawings,it"isto be expressly'understood that ths' drawing'sfare forthefipurposenof illustrapurpose reference should :belhadl to theappended claiins Referring now .to Athe drawings, wherein ,like

reference characters indicate .like parts. throughout theseveralviews:

Fig. 1 `isla planA view, with the casing and a portion of the upperrotorl shown4 in section; of a rotary compressonofthe positive displacement,4

helicaily ribbed rotor .typeembodying.v thenovel'A automatically balanced construction ofthefpresev ent invention;

Fig. 2 is a horizontal axialsection,-onV `an enlarged scale, of therotor assemblyfof Figli vwith the shaft shown `in-1full and/the partsrinl theirv normal, unexpanded positions;

Fig. 3 isan end Ielevatiomon avfurther en- A lai-ged scale, ofone fof thefsplit rings which' serve to i maintainy the `rotor 'body centered with respect to the shaft;

Fig. 4 is across `section ofthe-ringof Fig. 3-

taken on line 4 4 in the lattergure;

Fig. 5 isl an enlarged fragmentary axial secl` tional .view of the automatic balancing structure of Fig. 2 showingthe=parts in the'positions which they occupy `underfnormal temperature condi-` tions;

Fig; 6 is a `View similarto Fig; 5, but showing the parts inthe positions yoccupied when sub-V jected to' a relatively'hightemperature;`

Big5? isan end elevation of a Rootsitype rotar embodying the automatically balancedconstruc-l tien of theipresent'invention; and

Fig. 8 isa vertical axial section', with the shaft" shown in full, of the rotor assembly of Fig'.- 7 taken on line 8'- inthe latter figure.

The device illustrated vin Fig.` 1, representing one form of vgas handling apparatus'wherein the balancing arrangement of the present invention finds particular utility, is a rotary screwv type compressor of thecharacter disclosed-in' my prior Patent No. 2,511,878; datedJJune-20, 1950. In such a device, the detailed constructi-en ofvvhichfmay be freadily ascertained' from" my' aforesaid patent;v a pail1` ofv helically` ribbed rotors I I `(onlybnecf"which canZ be seen inthe neath that shown) are rotatably supported in a casing i2 'in intermeshed relationship, each rotor assembly'including 4a body portioni ifwhich isf formed with a single'screvr thread 'havingarunning lit' in the .casing i 2,- and a shaft.' |/i""'which` exten-'ls outwardly through'the ends of the'cas-' into detachable heads'.|5 and I6 wherein are mounted combination-*radial "and-fend thrust bearingsmll and" lr'ifor *the shaft: The shaft l i i ofthe upper rotor projects 'outwardlyof thefcasingA lhee d. 5 i 6" and fisadapted'. tolbe connectedlto a suitable source gof power.' for driving. f -the cornpressor, the driving torque being transmitted from the upper rotor to the lower one through timing gears I9 housed in the casing head I6.

The casing I2 is provided at one end (the right-hand end as viewed in Fig. 1) with a laterally extending intake conduit 20 and at the other end with an oppositely extending discharge conduit 2 I. The air or other gas to be compressed is supplied from the intake conduit 20 directly to a relatively large intake chamber 22 which is in permanent communication with the intake end of the gas transporting and compressing space 23 defined by the rotor threads and the surrounding wall of the casing I2. As the rotors turn, the

f gas is advanced by the rotor threads toward the left as viewed in Fig. 1 and, as the compressing space 23 gradually decreases in volume, is compressed against the inner vertical wall of a hollow casting 24 which is removably tted into the discharge end of the casing I2 and is provided with a suitable port (not shown) through which the compressed gas is intermittently delivered to thedischarge conduit 2i in the manner disclosed in my previously mentioned Patent No. 2,511,878.

The rotor body I3 of each rotor I I is preferably formed separately from its shaft I4 and fixed thereto for rotation therewith in any suitable manner, as by a key and keyway connection indicated at 25 in Fig. 2.

In certain installations, particularly where the rotors are of relatively large diameter and weight is an important factor, it is desirable that the screw threaded rotor bodies be made of a relatively light material, such as aluminum, even though the rotor shafts are made of steel. In a rotor assembly of this character, the heat generated by compression of the gas causes the aluminum rotor body to expand more than the steel shaft, particularly that portion of the rotor body adjacent the discharge end of the casing, with the result that the body becomes loose on the shaft and the rotor assembly is unbalanced. In order to remedy this defect in prior structures of the character described, novel means have been provided by the present invention for automatically maintaining the rotative balance of the rotor assembly in spite of the unequal expansion of the parts thereof under the influence of high temperatures.

In the embodiment illustrated in Figs. 1-6, a self-centering connection is provided between the rotor body I3 and shaft I4 at the discharge end of the rotor assembly which is so constructed that, although the aluminum rotor body may expand at an appreciably greater rate than the steel shaft when subjected to elevated temperatures, the two elements of the assembly are maintained coaxial with one another and no looseness is permitted to develop.

As shown best in Figs. 2, and 6, the shaft III has a portion 2l of reduced diameter at the discharge or hot end of the rotor assembly which extends into the bore of the rotor body I3 for a substantial distance, there being an inclined or beveled shoulder 23 'between the reduced diameter portion 27 and the main part of the shaft. The end of the rotor body I3 which surrounds the reduced portion 2'! of the shaft is provided with an inwardly projecting, straight-sided annular collar 29 of substantial axial extent, the internal diameter of said collar being such that, when the parts are subjected to normal temperatures, on the order of 70 F., the collar fits tightly about the reduced portion of the shaft. The collar 2B is so positioned that its inner or righthand radial edge 30 normally lies in substantially the same diametral plane as the junction between the reduced portion 2l and the inclined shoulder 23 of the shaft, while the outer or lefthand edge 3l of said collar is spaced inwardly from the outer end of the rotor body I3 by a distance substantially equal to the axial length of the shoulder 28.

Interposed between the shaft shoulder 23 and the surrounding portion of the rotor body is a split ring 32 having a triangular cross section of such shape and size that, at normal temperatures when the assembly is cool, the ring substantially iills the annular space defined by the beveled surface of shoulder 28, the inner radial edge B of the collar 29 and the axial lbore 33 of the rotor body. As indicated in Figs. 2 and 3, the split in ring 32 lies in a radial plane through the axis of the shaft, and when the parts are originally assembled, the portions of the ring on opposite sides of the split are in end-to-end contact. A second split ring 35, identical with ring 32 except that its beveled edge faces to the left instead of to the right, is housed in the annular recess in the end of the rotor body I3 abutting the outer or left-hand radial edge 3| of the collar 29, and is held in place by a sleeve 36 which surrounds the reduced portion 21 of the shaft between the outer end of the rotor body and the bearing I? in the casing head I5. rThe inner or right-hand end of sleeve 36 is provided with an inclined or beveled shoulder 3l of the same angularity as, but sloping oppositely to, the shoulder 28 on the shaft so as to cooperate with the beveled edge of the second split ring 35 in the same manner as the shaft shoulder 28 cooperates with the first split ring 32. The rotor body I3, shaft ld, split rings 32 and 35, sleeve 36 and the inner race of bearing I'l are held together in assembled, relatively non-rotatable relationship by a nut 32 which is threaded onto the outer end of shaft portion 2l and abuts said inner bearing race.

The split rings 32 and 35 and sleeve 3G are preferably made of the same material as the shaft I4 and its reduced portion 2l, steel of 300 Brinell hardness being an appropriate material for all of these elements when the rotor body I3 is of aluminum. In any event, the metal of the split rings and sleeve should have a coefficient of thermal expansion which is at least equal to that of the shaft metal and not greater than that of the rotor body.

The angularity of the shoulders 23 and 3i on the shaft and sleeve, respectively, and that of the beveled edges of the spit rings 32 and 35 is determined by the relationship between the diameter of the reduced portion 2l of the shaft and the axial length of the collar 29 of the rotor body. As indicated in broken lines in Fig. 2, the angularity of these inclined surfaces may be represented by the diagonals of a rectangle having adjacent sides equal to the diameter of shaft portion 2l and the axial length of collar 2S, respectively. Mathematically, the value of the angle of inclination of the shoulders 28 and 3'! with respect to the outer surface of the reduced shaft portion 2l, which is also the angle of the outer corners of the split rings 32 and 35, may be derived from the formula tan A=D /L, Where A is the angle in question, D is the diameter of the shaft portion 2l and L is the axial length of the collar 29. In the structure illustrated in Figs. 1 6, this angle may conveniently be established at 45, although it is evident that the angularity may be varied, as desired.

The method of operation of the unique selfaluminum and the specific grade of steel above mentioned, as long as the rotor body has a higher coefficient of thermal expansion than the shaft on which it is mounted.

Various other changes', which will now suggest themselves to those skilled in the art, may be made in the form, details of construction and arrangement of the parts without departing from the spirit of the invention. Reference is therefore to be had to the appended claims foi` a definition of the limits of the invention.

What is claimed is:

1. A rotor assembly comprising a shaft, a separately formed rotor body mounted on said shaft for rotation therewith, said shaft and rotor body being formed of different materials having different coefficients of thermal expansion, and means including at least one annular element interposed between said rotor body and shaft and displaceable both radially and axially relative to said shaft in response to the difference in thermal expansion of said rotor body and shaft for maintaining the latter in rotatively balanced relationship.

2. A rotor assembly comprising a shaft, a separately formed rotor body mounted on said shaft for rotation therewith, said rotor body being formed of a material having a higher coefficient of thermal expansion than that of said shaft, and means including at least one mechanically expansible member interposed between said rotor body and shaft for maintaining said rotor body concentric with said shaft when the assembly is subjected to elevated temperatures and the rotor body expands to a greater extent than the shaft.

3. A rotor assembly comprising a shaft, a sepa rately formed rotor body mounted on said shaft for rotation therewith, said rotor body being formed of a material having a higher coefficient of thermal expansion than that of said shaft, and means including a pair of mechanically expansible members interposed between said rotor body and shaft and displaceable in response to the difference in thermal expansion of said elements for maintaining said rotor body concentric with said shaft when the assembly is subjected to elevated temperatures and the rotor body expands to a greater extent than the shaft.

4. A rotor assembly comprising a shaft, a separately formed rotor body mounted on said shaft for rotation therewith, said rotor body being formed of a material having a higher coefficient of thermal expansion than that of said shaft, and means for maintaining said rotor body con'- centric with said shaft when the assembly is subjected to elevated temperatures and the rotor body expands to a greater extent than said shaft, said means including elements rotatable with said shaft forming a pair of axially spaced, oppositely inclined shoulders extending divergently from the axis of said shaft,- an annular portion of said rotor body projecting radially inwardly between said shoulders, and a pair of expansible rings interposed between and in contact with both said shoulders and the adjacent edges of said annular portion of the rotor body.

5. A rotor assembly comprising-a shaft, a separately formed rotor body mounted on said shaft for rotation therewith, said rotor body being formed of a material having a higher coefficient of thermal expansion than that of said shaft, and means for maintaining said rotor body concentric with said shaft when ther assembly is subjected to elevated temperatures and the rotor body expands to a greater extent than said shaft,

said meansincluding elements rotatable with said shaft forming a pair of axially spaced, oppositely inclined shoulders extending divergently from the axis of said shaft, an annular portion of said rotor body projecting radially inwardly between said shoulders, the edges of said annular portion being perpendicular to thc axis of said shaft, and a pair of split rings of triangular cross section interposed between and in contact with both said shoulders and the adjacent edges of said annular portion of the rotor body.

6. In a rotor assembly of the type including a shaft and a separately formed rotor body mounted on said shaft for rotation therewith, said rotor body being formed of a material having a higher coefficient of thermal expansion than that of said shaft, a self-centering connection between the shaft and rotor body effective to maintain the rotative balance of the assembly when subjected to elevated temperatures comprising means forming an inclined shoulder on said shaft, a sleeve on said shaft having a shoulder thereon of the same inclination as that on said shaft but sloping in the opposite direction and axially spaced therefrom, an annular portion of said rotor body projecting radially inwardly between said shoulders, and a pair of expansible members substantially filling the spaces between said shoulders and the adjacent edges of said annular portion of the rotor body when the rotor assembly is cool.

7. In a rotor assembly of the type including a shaft and a separately formed rotor body mounted on said shaft for rotation therewith, said rotor body being formed of a material having a higher coefficient of thermal expansion than that of said shaft, a self-centering connection between the shaft and rotor body effective to maintain the rotative balance of the assembly when subjected to elevated temperatures comprising means forming an inclined shoulder on said shaft, a sleeve on said shaft having a shoulder thereon of the same inclination as that on said shaft but sloping in the opposite direction and axially spaced therefrom, an annular portion of said rotor body projecting radially inwardly between said shoulders and in contact with said shaft when the rotor assembly is cool, the edges of said annular portion being perpendicular to the axis of said shaft, and a pair of split rings substantially filling the spaces between said shoulders and the adjacent edges of said annular portion of the rotor body.

8. A self-centering connection between the shaft and rotor body of a rotor assembly asdefined in claim 7 wherein the angle of inclination of said shoulders is such that the tangent of said angle is substantially equal to the ratio between the diameter of the shaft between said shoulders and the axial length of said annular portion of the rotor body.

9. A self-centering connection between the shaft and rotor body of a rotor assembly as dened in claim 7 wherein said sleeve and split rings are made of material having a coefficient of thermal expansion not greater than that of the rotor body and at least equal to that of said shaft.

10. A self-centering connection between the shaft and rotor body of a rotor assembly as defined in claim 7 wherein said sleeve and split rings are made of the same material as said shaft.

11. In a rotor assembly of the type including a shaft and a separately formed rotor body mounted on said shaft for rotation therewith, said rotor body being formed of a material having a higher coefficient of thermal expansion than that of said shaft, a self-centering connection between the shaft and rotor body effective to maintain the rotative balance of the assembly when subjected to elevated temperatures comprising a shaft portion of reduced diameter, an inclined shoulder formed on said shaft between said reduced portion and the remainder thereof, a sleeve on said reduced shaft portion axially spaced from said shoulder and having a shoulder on the end thereof of the same inclination as said first named shoulder but sloping in the opposite direction, an internal collar on said rotor body projecting radially inwardly between said shoulders and having a relatively tight t on said reduced shaft portion at normal temperatures, and a pair of split rings interposed between and in contact with both said shoulders and the adjacent edges of said collar.

12. In a rotor assembly of the type including a shaft and a separately formed rotor body mounted on said shaft for rotation therewith, said rotor body being formed of a material having a higher coeiiicient of'thermal expansion than that of said shaft, a self-centering connection between the shaft and rotor body effective to maintain the rotative balance of the assembly when subjected to elevated temperatures comprising a portion of reduced diameter at one end of said shaft, an inclined shoulder formed on said shaft between said reduced portion and the remainder thereof, a sleeve on said reduced shaft portion axially spaced from said shoulder and having a shoulder on the end thereof of the same inclination as said rst named shoulder but sloping in the opposite direction, an internal collar at the end of said rotor body surrounding the reduced shaft portion, said collar projecting radially inwardly between said shoulders and having a relatively tight t on said reduced shaft portion at normal temperatures, a pair of split rings interposed between and in contact with both said shoulders and the adjacent edges of said collar, and a nut on the outer end of said reduced shaft portion for holding said rotor body, shaft, sleeve and split rings in assembled, relatively non-rotatable relationship. g

GILBERT RATHMAN.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,442,254 Whiteld --.l May 25, 1948 

